My h18 hulls have become very thin from dragging it over the sand. The area in question is just in front of the daggerboard wells and show almost transparent when a flashlight is shown through . Would just a few layers of gelcoat do the job or should layers of fiberglass on the inside do the trick? (or both?).Has this been discussed elsewhere on the forum? If so, where? Thanks.....dj

As a general rule, you should replace gelcoat where gelcoat has been worn away and replace fiberglass where fiberglass has been worn away. In other words, if you've worn down into the hulls to the point that the fiberglass is paper thin, you need to build back up with fiberglass, not just cover with gelcoat. Fiberglass is a structural material, gelcoat is not. I would not add fiberglass to the inside of the hull. I would add it to the outside of the hull where it was removed so that you rebuild the hull to its original shape.

Also, trying to judge the fiberglass thickness by shining a light through is really not accurate. Once the gelcoat is worn away, the light will easily pass through the glass since there's no foam core at the bottom of the hull and the resin and glass are both translucent. It may appear to be thinner than it actually is.